Open-system authentication can be referred to as no authentication, since no actual authentication and user credential validation takes place. A client user requests (and is granted) authentication with no credential exchange.
Such a security-free convention may be appropriate in certain guest networks wherein no proprietary information purposely exposed to requesting clients, and their access to the controller, service platform or access point managed network is temporary and closely administrated.
Note
Although None implies no authentication, this option is also used when pre-shared keys are used for encryption (thus the PSK in the description).